This invention relates to heat sinks, and more particularly to heat sinks for memory modules.
Heat sinks have been widely used to assist in cooling electrical components. Some microprocessors have heat sinks attached to allow for higher-frequency operation. Other components such as memory modules may also benefit from heat sinks.
Most personal computers (PC's) are shipped with sockets for memory modules so that their owners can later add additional modules, increasing the memory capacity of the PC. Other non-PC devices may also use memory modules designed for PC's. High-volume production and competition have driven module costs down dramatically, benefiting the buyer.
Memory modules are made in many different sizes and capacities, with the older 30-pin modules replaced by 72-pin, 168-pin, and other size modules. The “pins” were originally pins extending from the module's edge, but now most modules are leadless, having metal contact pads, fingers, or leads. The modules are small in size, some being about 5.25 inches long and 1.2 or 1.7-inches high.
The modules contain a small printed-circuit board (PCB) substrate, typically a multi-layer board with alternating laminated layers of fiberglass insulation and foil or metal interconnection layers. Surface mounted components are soldered onto one or both surfaces of the substrate. Memory integrated circuits (IC's) or chips are commonly packaged in inexpensive surface-mount packages such as small-outline J-leaded (SOJ) packages, plastic leaded chip carriers (PLCC's), thin small-outline packages (TSOP) or small-outline (SO) packages. The number of memory chips in a module depends on the capacity and the data-width of the memory chips and the size of the memory module.
FIG. 1 is a diagram of a memory module with dynamic-random-access memory (DRAM) chips. The memory module contains substrate 10, with surface-mounted DRAM chips 20 mounted directly to the front surface or side of substrate 10, while more DRAM chips (not visible) are usually mounted to the back side or surface of substrate 10. Metal contact pads 12 are positioned along the bottom or connector edge of the module on both front and back surfaces. Metal contact pads 12 mate with pads on a module socket to electrically connect the module to a PC's motherboard. Holes and/or notches 14, 16 are sometimes used to ensure that the module is correctly positioned in the socket. For example, notch 14 can be offset from the center of substrate 10 to ensure that the memory module cannot be inserted backwards in a socket. Notches 16 match with clamps of the module socket to ensure that module is securely positioned in the socket.
As processor speeds have increased, the need for faster memory has become more critical. Various bandwidth-enhancing methods and memory interfaces have been used. Memory chips have higher densities and operate at higher frequencies than before, producing more waste heat from the memory chips. There is a need to remove this waste heat from memory modules.
Various heat sinks designed for memory modules are known. See for example U.S. Pat. Nos. 6,362,966, 6,424,532, and 6,449,156, among others. Clamp-on heat sinks for memory modules are also known. For example, Corsair Memories makes a heat sink that fits over the front and back surfaces of a memory module and is held in place by a wire clip over the top edge. OCZ Technology produces a copper heat sink with wider metal bands that clip the heat sink to over the front and back surfaces of the memory module. While useful, these clip-on and clamp-on designs can exhibit a flimsiness or lack of rigidity that can make the memory modules appear cheaply made.
Some memory-module heat sinks feature a closed-top design that prevents air flow in the small gaps between the heat sink and the memory module substrate. Often the entire top edge of the heat sink is closed, providing no path for air to flow under the heat sink other than back out the bottom edge, which is usually open. Sides may be open or partially open, but the sides are much smaller than the top and bottom edges of the memory module, limiting the possible air flow.
What is desired is a heat sink designed specifically for memory modules. A rigidly attached heat sink for memory modules is desirable. A heat sink with a more efficient air flow across memory chips on a memory module is also desirable.